This invention relates generally to a driver circuit for driving capacitive loads, and more particularly to a driver circuit including boost and feedback portions which result in a faster output rise time and reduce the propagation delay.
Driver circuits which drive, for example, MOS field-effect-transistors (MOSFETS) typically include an output node, a high/side driver for raising the potential of the output node, a low/side driver for reducing the potential of the output node, and an input stage for controlling the high and low side drivers.
It is known, for example, to use a regenerative trigger circuit with limited gain as the top side driver. The trigger circuit includes a PNP current mirror circuit and one or more NPN transistors coupled to the output node. A small portion of the NPN collector current is fed back to the PNP mirror so as to provide additional base current to the NPN devices. Thus, the potential to the output node will begin to rise before current regeneration in the trigger circuit can occur thus degrading output rise time. Additionally, the drive current to the PNP mirror circuit will be affected by output loading; i.e. while loads will degrade output rise time.
U.S. Pat. No. 4,701,631 entitled MONOLITHICALLY INTEGRATED CONTROL CIRCUIT FOR THE SWITCHING OF TRANSISTORS discloses a driver circuit for driving inductive loads. The driver disclosed in this patent includes a boost circuit which provides a boost current pulse to the top side driver. The length o this boost pulse is determined by an RC time constant, not by the voltage on the output node. Furthermore, since the load is inductive, there is little output current during the rise time. With a capacitive load, however, there is an immediate need for a large output current.